Optical target sensor

ABSTRACT

An optical target sensor mounted on a projectile, produces a fuzing signal when two light sensitive devices which are mounted on the projectile sense light pulses which are separated by a fixed time interval. One of the light sensors is mounted to be exposed to light pulses which are projected towards and beyond the projectile by an illuminator. The other light sensor is mounted to be exposed to the illuminator light which is reflected from the general target area. The range at which a fuzing signal occurs is controlled by setting the time difference required between the two pulses. No radiation occurs from the target sensor because it receives its signals as a result of radiation from the illuminator. The light projector or illuminator may comprise a pulsed laser.

1Jited States Patent [191 Brenner OPTICAL TARGET SENSOR [75] Inventor: Charles Herbert Brenner,

Scottsdale, Ariz.

[73] Assignee: Motorola, Inc., Franklin Park, Ill.

[22] Filed: Mar. 19, 1971 [21] Appl. No.: 126,232

[52] US. Cl 102/70.2 P, 244/3.16 [51] Int. Ch... F42c 13/02, F42c 11/06, F42c 15/40 [58] Field of Search l02/70.2 P; 244/3.l6, 3.17

[56] References Cited UNITED STATES, PATENTS 3,527,167 9/1970 Morse 102/702 R 3,129,424 4/1964 3,538,506 9/1968 3,040,661 6/1962 3,455,243 7/1969 AIRBORNE lLLUMINATOR June 26, 1973 Primary ExaminerSamuel Feinberg Assistant Examiner-Thomas H. Webb Attorney-Mueller & Aichele [5 7] ABSTRACT An optical target sensor mounted on a projectile, produces a fuzing signal when two light sensitive devices which are mounted on the projectile sense light pulses which are separated by a fixed time interval. One of the light sensors is mounted to be exposed to light pulses which are projected towards and beyond the projectile by an illuminator. The other light sensor is mounted to be exposed to the illuminator light which is reflected from the general target area. The range at which a fuzing signal occurs is controlled by setting the time difference required between the two pulses. No radiation occurs from the target sensor because it receives its signals as a result of radiation from the illuminator. The light projector or illuminator may comprise a pulsed laser.

8 Claims, 2 Drawing Figures OPTICAL TARGET SENSOR BACKGROUND This invention relates to an optical target sensor to be mounted on a projectile which will produce a fuzing signal while the projectile is still in flight and at a predetermined distance from the target. Typically, the fuzing signal is used to detonate the explosive charge contained within the projectile body.

In accordance with the prior art, a radio transmitter and receiver are mounted on a projectile. The transmitter transmits a radio wave in a forward direction towards the target and the radio wave is reflected back to the projectile upon reflection from the target. In a known manner, the fuzing signal is produced when the time lag of received reflected waves with respect to the transmitted waves indicates that the projectile is a given distance from the target. The prior art called a target sensor or a proximity fuze if a safmg and arming device and detonator are included, is costly, complicated, bulky and requires a large battery since the battery must supply power to both the transmitter as well as the receiver. Furthermore, jamming waves due to other radiation sources in the area may cause a fuzing signal to be produced when the projectile is a long way from the target. Furthermore, each projectile transmits its own wave which may be received by another projectile, whereby the projectile may produce a fuzing signal before the desired distance to the target is reached.

It is the object of this invention to provide single target sensor that can be carried on a projectile such as a shell or rocket which will produce a fuzing signal at a desired distance in front of a target without actively radiating any energy.

It is a further object of this invention to provide such a target sensor that is simpler, less costly, more reliable and harder to jam than known suchtarget sensors.

SUMMARY In accordance with this invention, the projectile carries two photosensitive devices, and means are mounted on the projectile to cause light from in front of the projectile to be applied to one of the photosensitive devices and other means are mounted on the projectile to cause light from in back of the projectileto be applied to the other photosensitive device. A light source which may be a pulsing laser projects light in a manner so that the projectile and the target are illuminated by the light provided by the laser. When the light pulse which hits the target and is reflected back to the projectile has the desired time delay with respect to the light that hits the projectile directly from the light source, the target sensor produces an output. The distance from the target that the target sensor produces a fuzing signal is dependent on the time delay required between the two light pulses. By varying the required time delay, fuzing signals can be produced when the projectile is several hundred feet to only a few feet from the target. The only electronics necessary on the projectile are two receivers and a coincidence detector and fire pulse generator, whereby the electronics on the projectile are simple and inexpensive.

DESCRIPTION The invention will be better understood upon reading the following description in connection with the accompanying drawing in which:

FIG. 1 illustrates the target sensor of this invention as being in operation, and

FIG. 2 is a block diagram of a circuit for use on the projectile as shown in FIG. 1.

A projectile 10 is shown in flight towards the target area 12. The front part of the projectile 10 which contains the target sensor 14, is shown in cross section to illustrate the apparatus carried thereby. The projectile body 10 which carries the explosive charge (not shown) is shown partly in section and most thereof is broken away since the invention does not depend on the projectile portion 10 or on its contents. A light source 16 which may be a laser projects light beams 18 which may be in the ultraviolet, visible, or infrared wave length region, having a pulse width which may be only a few nanoseconds to several microseconds wide and pulse repetition rate of 10 pulses per second or greater towards the projectile 10 and beyond the projectile 10 towards the target area 12. The light beams 18 have a spread such that the projectile 10 is in the beam while the projectile takes its curved path towards the target and the target area is also illuminated by the beam 18. Therefore, as will be more fully disclosed, the back of the projectile l0 and the target area 12 are illuminated by the laser device 16 and light pulses reflected by the target area illuminates the front of the projectile which contains the target sensor 14. As shown in the drawing, the laser 16 is said to be airborne. When airborne, the projectile and the means for projecting it will also be carried by the airborne vehicle. However, the light source and the projectile projecting means may be stationary or may be mounted on a land or sea vehicle.

The projectile 10 carries two optical systems, one for receiving the light reflected from the target area 12 and one receiving the light directly from the laser 16. A light sensitive detector 20 is used to detect the reflected light 13 from the illuminated target area 12.

A lens 24 and optical reflecting cone 25 which are both coaxial with the projectile 10 extends through the forward end of the target sensor 14 and concentrates light on the light sensitive photodetector 20. The inner surface of the cone 25 may be plated with light reflect- .ing material which efficiently reflects the light of the wavelength of the beam 18 and the photodetector 20 is chosen to be sensitive to this wave length of light. While the cone 25 does not project an image on the light sensitive device, it does act as an efficient light collector.

Another light sensitive photodetector 26 is mounted centrally on the projectile 10 but behind the photodetector 20. The photodetectors 20 and 26 are separated from each other by opaque walls 28. A light collector 30 for the direct illumination 18 has cylindrical shape and operates similar to a periscope of revolution. The flat top portion 33, flat bottom portion 32, conical section 36 at the center of light collector 30 and the tapered outer edge 37 are all reflectively coated by a material which is highly reflective at the wavelength emitted by the illuminator 16. The only regions of the light collector 30 which are not reflectively coated is a small toroidal region 38 where the direct light 18 enters and a small circular region 39 centered on the axis of the projectile and located on the top side of the light collector 30 where light leaves and is incident on the photodetector 26. The outside edges 38 of the collector 30 are not covered with light reflecting material whereby light from the back of the projectile 10 hits the exposed surface 38 and the light is directed, after multiple reflections to the photodetector 26. As noted, the edges of the light collector 30 extend beyond the outside of the diameter of the projectile body so that light from the laser 16 will reach the photodetector diode 26.

The target sensor 14 is normally located at the front of the projectile 10. For complete fuzing system a battery and safe arming device would be added but they are not described because they are not pertinent to this disclosure. The electronic equipment that is necessary for the target sensor 14, is located in the volume between the two walls 28. The electronics required for the target sensor 14, shown by the typical block diagram in FIG. 2, is not critical in that many known electronic devices are useable. The output of an optics and photodetector circuit 50, which may include the photodiode 20, is applied to a video amplifier 52. The video amplifier 52 produces its fixed maximum output upon application thereto of a small signal and this output is not increased by an amplitude above a small value of the input signal. The output of the video amplifier S2 is a rectangular wave form since the reflected light received from the target area 12 is a pulse form. This pulse may be applied to a monostable multivibrator 54. As will be noted, for certain purposes, the multivibrator 54 may be omitted. The output of the monostable multivibrator 54 is applied to one input of a coincidence detector 56. The output of the optics and photodetector circuit 58 which may include the photodiode 26 is applied to a video amplifier 60 which is like the video amplifier 52 whose output is applied to the other input of the coincidence detector 56. When two pulses are coincident in the coincidence detector 56, the coincidence detector 56 activates a tire pulse generator 62.

As noted above, the monostable multivibrator 54 may be omitted in which case the output of the video amplifier 52 is applied directly to an input of the coincidence detector 56. When the monostable multivibrator is omitted, a pulse directly from the laser 16 and the same pulse reflected by the target at 12 are supplied to the coincidence detector 56. For example, if the illuminator 16 has a pulse with duration of 10 nanoseconds, pulse coincidence occurs when the projectile 10 is approximately feet slant range from the target area 12. If slant ranges from the target of about 300 feet are desired the monostable multivibrator S4 is included between the video amplifier 52 and the coincidence detector 56. This monostable multivibrator 54 is adjusted to produce a pulse duration of about 600 nanoseconds. When the leading edge of the reflected pulse is coincident with the leading edge of the pulse produced by the multivibrator 54, the pulse coincidence detector 56 activates the fuzing generator 62.

While the projectile is shown as a right cylinder, it can be of any shape that projectiles may take. While the laser illuminator 16 and therefore the projector for the target sensor 14 is normally on the airborne launch vehicle it could be located on other airborne vehicles. While the light collector 30 that collects the direct rays 18 is shown permanently deployed beyond the surface of the projectile 10, the light collector could be deployed after launch or be located at the rear end of the projectile 10.

What is claimed is:

1. In a projectile exploding system including means for transmitting light pulses to a projectile and to a target,

an explosive projectile portion for travelling toward said target having a charge carrying portion and a front or nose portion, said front or nose portion including:

two photosensitive devices,

an opaque member between said photosensitive devices,

a hollow cone extending from the front of said nose portions towards one of said photosensitive devices, the large end of said cone being towards said front,

a transparent layer extending across the rear of said front portion, said other photosensitive device being in light transfer relation to the center of a side of said transparent layer, the edges of said transparent layer extending beyond said charge carrying shell portion,

both sides of said transparent layer except for said center of said side of said center of said side of said transparent layer and an annular portion of the other side of said transparent layer being coated with a light reflective layer,

the uncovered portion of said other side of said transparent layer being shaped and positioned to receive light from behind said charge carrying shell portion,

and means on said projectile to explode said charge upon light being exposed to both of said photosensitive devices.

2. The invention of claim 1 in which the center of said other side of said transparent layer is formed to direct light to said second photosensitive device.

3. The invention of claim 1 in which a laser producing pulsed light is provided to project light towards the back of said projectile whereby light from said laser is applied to said second photosensitive device and light reflected from a target is applied to said one photosensitive device.

4. In a projectile exploding system including means for transmitting light pulses to a projectile and to a target,

an explosive projectile portion for travelling toward said target including:

two light sensitive devices on said projectile portion,

means on said projectile portion for receiving light pulses transmitted from said transmitting means at a particular instant and applying same to one of said light sensitive devices,

means on said projectile portion for receiving light pulses transmitted from said transmitting means at said particular instant but after reflection from said target and applying same to the other of said light sensitive devices,

means for developing a first signal upon receipt of a direct light pulse by said one of said light sensitive means,

means for developing a second signal upon receipt of a reflected light pulse by said other one of said light sensitive means,

time delay means for receiving said first signal and for developing a third signal in response thereto after a predetermined time delay,

coincidence means for receiving said third and said second signals and developing an output signal when said third and said second signals coincide, directed optical system. and 7. The system according to claim 6 wherein said rearmeans responsive to said output signal for generating wardly directed optical system comprises a circular a firing signal. prism having a peripherally circular light receiving sur- 5. The system according to claim 4 wherein said time 5 face and a centrally circular light directing surface, and delay means comprises a monostable multivibrator. said forwardly directed optical system comprises an 6. The system according to claim 4 wherein said optical lens. means for receiving said light pulses transmitted from 8. The system according to claim 4 wherein said two said source comprises a rearwardly directed optical syslight sensitive devices comprise two photosensitive ditern, and 10 odes spaced axially from each other and including an wherein said means for receiving said pulses of light opaque surface between them.

reflected from said target comprises a forwardly 

1. In a projectile exploding system including means for transmitting light pulses to a projectile and to a target, an explosive projectile portion for travelling toward said target having a charge carrying portion and a front or nose portion, said front or nose portioN including: two photosensitive devices, an opaque member between said photosensitive devices, a hollow cone extending from the front of said nose portions towards one of said photosensitive devices, the large end of said cone being towards said front, a transparent layer extending across the rear of said front portion, said other photosensitive device being in light transfer relation to the center of a side of said transparent layer, the edges of said transparent layer extending beyond said charge carrying shell portion, both sides of said transparent layer except for said center of said side of said center of said side of said transparent layer and an annular portion of the other side of said transparent layer being coated with a light reflective layer, the uncovered portion of said other side of said transparent layer being shaped and positioned to receive light from behind said charge carrying shell portion, and means on said projectile to explode said charge upon light being exposed to both of said photosensitive devices.
 2. The invention of claim 1 in which the center of said other side of said transparent layer is formed to direct light to said second photosensitive device.
 3. The invention of claim 1 in which a laser producing pulsed light is provided to project light towards the back of said projectile whereby light from said laser is applied to said second photosensitive device and light reflected from a target is applied to said one photosensitive device.
 4. In a projectile exploding system including means for transmitting light pulses to a projectile and to a target, an explosive projectile portion for travelling toward said target including: two light sensitive devices on said projectile portion, means on said projectile portion for receiving light pulses transmitted from said transmitting means at a particular instant and applying same to one of said light sensitive devices, means on said projectile portion for receiving light pulses transmitted from said transmitting means at said particular instant but after reflection from said target and applying same to the other of said light sensitive devices, means for developing a first signal upon receipt of a direct light pulse by said one of said light sensitive means, means for developing a second signal upon receipt of a reflected light pulse by said other one of said light sensitive means, time delay means for receiving said first signal and for developing a third signal in response thereto after a predetermined time delay, coincidence means for receiving said third and said second signals and developing an output signal when said third and said second signals coincide, and means responsive to said output signal for generating a firing signal.
 5. The system according to claim 4 wherein said time delay means comprises a monostable multivibrator.
 6. The system according to claim 4 wherein said means for receiving said light pulses transmitted from said source comprises a rearwardly directed optical system, and wherein said means for receiving said pulses of light reflected from said target comprises a forwardly directed optical system.
 7. The system according to claim 6 wherein said rearwardly directed optical system comprises a circular prism having a peripherally circular light receiving surface and a centrally circular light directing surface, and said forwardly directed optical system comprises an optical lens.
 8. The system according to claim 4 wherein said two light sensitive devices comprise two photosensitive diodes spaced axially from each other and including an opaque surface between them. 